The electronic structure of several alkyl-, N_bis(trimethylsilyl)methyl- (BTMSM), and C_phenyl-substituted imines 1 - 11 have been determined by ab-initio 3-21G* calculations. The calculations reproduce with good accuracy the available geometry of methyleneimine, 1, obtained by microwaves spectroscopy1 and ab-initio 6-31G** calculations2 as well as the outermost energy levels experimentally determined by UPS for several derivatives. The analysis of the results of the calculations indicate that alkyl substitution of 1 at the nitrogen atom reduces the charge separation at the double bond increasing stabilisation, while substitution at the carbon atom has the opposite effect. Steric hindrance of the substituent(s) and the energy gaps between filled (nitrogen lone pair, HOMO, and πCN) and virtual (π*CN) orbitals play a secondary role on stability. All the BTMSM and phenyl derivatives studied are stable in air at room temperature irrespective of other substituents present. Our analysis indicates that these substituents change the energy, the ordering and the localisation properties of the valence MOs. In particular, the nitrogen lone pair orbital is no more the HOMO.
Ultraviolet Photoelectron, Electron Transmission and ab-initio Study of the Factors Determining the Stability of imines
DAL COLLE, Maurizio;DISTEFANO, Giuseppe;
1994
Abstract
The electronic structure of several alkyl-, N_bis(trimethylsilyl)methyl- (BTMSM), and C_phenyl-substituted imines 1 - 11 have been determined by ab-initio 3-21G* calculations. The calculations reproduce with good accuracy the available geometry of methyleneimine, 1, obtained by microwaves spectroscopy1 and ab-initio 6-31G** calculations2 as well as the outermost energy levels experimentally determined by UPS for several derivatives. The analysis of the results of the calculations indicate that alkyl substitution of 1 at the nitrogen atom reduces the charge separation at the double bond increasing stabilisation, while substitution at the carbon atom has the opposite effect. Steric hindrance of the substituent(s) and the energy gaps between filled (nitrogen lone pair, HOMO, and πCN) and virtual (π*CN) orbitals play a secondary role on stability. All the BTMSM and phenyl derivatives studied are stable in air at room temperature irrespective of other substituents present. Our analysis indicates that these substituents change the energy, the ordering and the localisation properties of the valence MOs. In particular, the nitrogen lone pair orbital is no more the HOMO.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
